Semiconductor processing typically involved the formation of one or more layers on a semiconductor substrate. For example, silicon epitaxy, sometimes called epi, was a process in which one or more layers of single-crystal (monocrystalline) silicon were deposited on a monocrystalline silicon wafer.
To form a layer on a substrate, a process gas, typically a reactive gas, was introduced into a reactor containing the substrate. The process gas reacted to form the layer on the substrate.
As the art moves towards reduced feature size integrated circuits, it has become increasingly important that the deposited layer has a uniform thickness. One primary parameter, which affected the thickness uniformity of the deposited layer, was the flow characteristics of the process gas into and through the reactor. These flow characteristics were controlled to a large extent by the gas injectors through which the process gas was introduced into the reactor.
To obtain the desired thickness uniformity, the gas injectors were calibrated. Calibration was typically an iterative manual process in which a first layer was deposited on a first test substrate, the thickness uniformity of the first layer was measured, and the gas injectors were manually adjusted in an attempt to improve the thickness uniformity. A second layer was then deposited on a second test substrate, the thickness uniformity of the second layer was measured, and the gas injectors were again manually adjusted. This trial and error manual procedure was repeated until the desired thickness uniformity was obtained.
To allow the gas injectors to be calibrated in the above manner, the gas injectors had to be readily and repeatably adjustable. Finn et al., U.S. Pat. No. 5,843,234, which is herein incorporated by reference in its entirety, teaches a gas jet assembly in which the direction of a nozzle of the assembly was controlled by a positioning device. By manually adjusting micrometer knobs of the positioning device, the direction of the nozzle, and therefore the direction in which process gas was introduced into the reactor, was controlled.
To adjust the micrometer knobs of the positioning device, the person who operated the reactor (the operator) had to physically go to the positioning device and turn the micrometer knobs by hand. This required the operator to leave the reactor controls temporarily unattended, which was undesirable. Further, turning the micrometer knobs by hand was relatively labor intensive and carried an inherent chance of operator error in micrometer knob adjustment.
The gas jet assembly of Finn et al. pivoted the nozzle relative to the reactor. Although allowing for pivoting of the nozzle, the gas jet assembly did not allow the nozzle to be moved in and out of the reactor. However, it is desirable to not only be able to control the direction of the process gas into the reactor, but also to be able to control the location within the reactor at which the process gas is introduced.
It was also important to avoid contamination of the reactor to allow high purity layers to be deposited. One potential source of contamination was the metal, e.g., stainless-steel, of the nozzle. In particular, the metal nozzle was often etched during processing, and this etched metal contaminated the deposited layer. To avoid etching of the metal nozzle, shielding was used in an attempt to isolate the metal nozzle from the activated process gas in the reactor. Although the shielding was relatively effective, etching of the metal nozzle was observed depending upon the particular process performed.